Modern containerships sometimes have the need to transport outsized and break-bulk cargo which does not fit into standard containers.
From prior art it is known that many solutions have been attempted in order to satisfy this need, almost all of them failed to achieve this goal. Presently only FlatRacks and gigantic containers named SeaShed are in limited use.
The main drawback of SeaSheds used for containership operations is the considerable loss is ship's container capacity which is equal to the full volume of SeaSheds when they are left in the hold, and the ship is back to exclusive container handling mode of operation. Among the other SeaShed disadvantages are the reduction in work-thru opening by 40% and high initial and maintenance cost.
The main drawback of the FlatRacks used for containership operations is also the substantial loss in ship's container capacity (one container for each two Flatracks left in the cellular hold). Comparative with SeaSheds, the FlatRacks require considerable additional handling during the general cargo mode of operation. Each time an access to the lower level is required all FlatRacks have to be removed from the hold and storred in some place. Besides complicating the cargo handling operation, this increases ship loading or unloading time.
The portable cargo deck described by U.S. Pat. No. 4,130,075, in comparison with SeaSheds and FlatRacks, requires much less space in order to be stored in the ship hold, however, it has the same drawback as the FlatRack in handling. The patented portable cargo deck also has to be removed from the hold each time access to lower deck is required.
Additional serious drawback of this portable deck is the need for a special hoisting device to lift and operate it. This limits its wide use to a few designated lines.